The present invention relates to transmission of digital data and more particularly to a system for reliably sending digital data over a channel where the signal may be subject to degradation during transmission.
Moving data from place to place electronically has become a vast enterprise in modern society. Telephones are used to transport voice signals between callers. Facsimile machines are employed to send documents to remote sites. Computers exchange digital data over modems. Radio signals broadcast audio programming to listeners. Television transmissions convey video signals to viewers in almost every home.
A variety of mechanisms or channels are available to send the different types of data. For instance, telephone calls, facsimile transmissions and modem transfers of digital data all can be completed over plain old telephone service (POTS) lines. Radio and television broadcasts are normally broadcast from transmission towers and satellites and sent over cable systems. With each of these channels, the data carrying capacity, or bandwidth, is governed by the nature of the data normally sent over the channel. Thus, POTS, being adapted to transmit voice data, has a relatively low bandwidth while typical television broadcast channels have relatively high bandwidth in order to convey the high volume of data inherent in a video signal.
In addition to considerations of bandwidth, the type of data that can be transmitted over a given channel is governed by whether or not the channel is bi-directional. Of the three main data transmission systems found in most residencesxe2x80x94telephone, radio frequency broadcast and cablexe2x80x94only telephone is inherently bi-directional. Thus, although other technologies are being developed, the telephone has been the channel of choice when data must be transmitted bi-directionally to and from a residence.
With the advent of the Internet, there has been explosive growth in the number of people that use their phone lines to access digital data from resources available on line. These resources include World Wide Web pages providing access to various types of digital data, such as still images and audio and video content. In some cases, the amount of data to be transferred challenges the bandwidth available on phone lines. In other cases, so many users are accessing the same data, that the separate repetitive transfer of the data to each of the users independently is inefficient.
One system in which both the bandwidth and repetitive transfer issues arise is the WEBTV(copyright) Internet access network. (WEBTV is a registered trademark of WebTV Networks, Inc. of Mountain View, Calif.) The WEBTV Internet access network includes a large number of Internet terminals, also referred to as client terminals, and at least one Internet Server. While the client terminals can access the Internet directly under some circumstances, the server provides a convenient standardized interface to facilitate access of the Internet by the client terminal. The server also offers supplemental services, such as email, news reports, television program guides and enhanced access to certain Web pages. In the course of carrying out these supplemental services, substantial quantities of individualized or private data, and broadly applicable or public data, must be downloaded to the client terminals.
With the current WEBTV system, supplemental services data is downloaded in advance during low-use periods to the extent possible. For instance, WEBTV client terminals are configured to automatically call into the server during the night to check for email and receive other information. However, because this process must be individually repeated for each client terminal, substantial telephone costs may be incurred. In addition, in some cases the quantity of data to be retrieved is so large that long periods of time are required to complete the download.
The present invention includes a system for distributing digital data over a video channel to a plurality of remotely located clients, such as WEBTV client terminals. The system involves selecting a set of digital data to be distributed, for instance, client terminal software updates or electronic programming guides, and converting the data to an intermediate format compatible with video broadcast. The intermediate data is then broadcast over a video channel during a time when no video content is being transmitted so that the intermediate format data takes the place of the video content. The intermediate format data is received at a remotely located client terminal where the set of digital data is recovered.